Method of forming intra-aortic balloon catheters

ABSTRACT

A method of forming intra-aortic balloons includes forming a balloon blank having a sleeve section at its proximal end. To reduce the diameter of the sleeve section of the balloon, the sleeve section is stretched longitudinally by gripping a first portion of the balloon blank at the distal end of the sleeve section, gripping a second portion of the balloon blank at the opposite end of the sleeve section and moving at least one of the gripped portions away from the other so as to reduce the diameter of the sleeve section. A heating element is positioned within the sleeve section to relieve the stress in the sleeve after stretching, by heating the sleeve section. The sleeve section is then cooled in order to preserve the sleeve section in its reduced diameter state thereby forming an intra-aortic balloon having a balloon blank with a reduced diameter sleeve section.

This application is a divisional of Ser. No. 08/210,611 filed Mar. 18,1994 which is a Continuation-In-Part of Ser. No. 08/170,513 filed Dec.20, 1993, both of which are now abandoned.

FIELD OF THE INVENTION

This invention relates to intra-aortic balloon pumps and particularly toimproved intra-aortic balloon pump catheters.

BACKGROUND OF THE INVENTION

Intra-aortic balloon pumps (IABP) are used to provide counter pulsationwithin the aorta of ailing hearts over substantial periods of time, e.g.to provide ventricular assistance during cardiogenic shock, low cardiacoutput in post-operative care, weaning from cardiopulmonary bypass,treatment for refractory unstable angina, and other circumstances ofsub-normal cardiac function. Such pumps of the type involved in thisinvention include a flexible intra-aortic balloon (IAB) which is readilyinflatable under low pressure to substantial size and displacement. Theballoon is mounted on a catheter device used for insertion of theballoon into a remote artery, typically a femoral artery, and throughthe intervening vascular system of the patient to the aortic pumpingsite while the balloon is deflated and furled. This requires insertionof the furled large capacity balloon through a small insertion passage,e.g., a small puncture opening or through an introducer cannula into theselected artery, and then sliding-threading of the catheter and furledballoon through tortuous lumen passageways of the patient's vascularsystem over a guidewire to the pumping site, e.g. from insertion into anartery in the groin area to the patient's descending aorta. At thepumping site, the balloon is unfurled and then successively and rapidlyinflated and deflated in synchronism with the patient's cardiacpulsation rates over extended periods of time in a knowncounterpulsation technique to enhance cardiac output. Thus, use of anIABP requires forceful sliding insertion of a relatively large balloonthrough a small insertion opening and tortuous arterial lumens, whichmay be randomly narrowed by arteriosclerotic deposits of plaque, andsubsequent unfurling and reliable pulsation operation at heartbeat ratesover substantial periods of time, e.g. for several days.

It will be appreciated that the circumstances and requirements ofinsertion and use of intra-aortic balloon pumps provide numerousconflicting parameters. Significant aspects of these conflictingparameters are related to the fact that the inflated but unstretcheddiameter of the balloon is much larger than the diameter of theinsertion site, which may be percutaneous, and larger than at leastportions of the lumen of the vascular system through which it is to bethreaded. This requires that the balloons be furled for insertionthrough passageways which are of very small inside diameter (ID)relative to the size of the balloon when opened. The related catheterequipment typically must include dual concentric lumens, including aninner lumen passageway to serve functions such as engaging over aguidewire, sensing values in the aorta, e.g. arterial pressure, and/oradministration of medicaments. A surrounding annular passageway betweenthe inner and outer lumens must be of a size adequate to shuttle anoperating gas such as helium at rates to obtain the rapid repetitiousexpansion and collapse of the balloon necessary for the pumping functionin counterpulsation to the patient's heart.

The aforenoted parameters for intra-aortic balloon catheters haveresulted in these catheters being of significant complexity ofconstruction and attendant substantial size, i.e. substantial effectivediameter of the catheter structure during insertion as well as duringthe periods of pumping operation within the patient's vasculature. Asignificant potential complication during use is associated with limbischemia due to size mismatch between the overall size (diameter) of thecounter pulsation catheter and the effective lumen size of the patient'svasculature through which the catheter must pass and in which it mustremain during the period of pumping assistance. Heretofore, the fullfeatured IAB catheter systems available on the market have been ofnominal 9 French (Fr) size or larger. The Fr size designation of an IABCrefers to the approximate size of the outer lumen. Thus, for example,while 9 Fr literally is about 0.118" diameter, catheters designated as 9Fr may have outer lumens which slightly exceed that dimension, e.g., upto about 122". Further, such catheters may include balloons whichoriginally were furled to about 0.126" outer diameter and in which thefurling has relaxed to about 0.144" outer diameter in their packagingsheaths. In any event, reduction in size of intra-aortic ballooncatheters and introducer systems would improve systemic flow to limbs atrisk.

However, as indicated above the insertion of an IAB catheterintrinsically involves pushing the device along a tortuous path throughthe patient's vasculature. This requires applying and transmittingcompressive forces through the very slender "column" structure of thecatheter, which requires a significant degree of stiffness in thecatheter. The catheter also must flex or bend to follow the desired paththrough the patient's vasculature without undue lateral reactive forcewhich could cause trauma to the vessels. Thus IAB catheters should havea high degree of stiffness over a wide range of bending angles, whileproviding flexibility to follow tortuous paths along which the IABcatheter is being pushed. These characteristics are measures of the"pushability" and "trackability" of the catheter, e.g., to follow aguide wire when pushed therealong over a tortuous path withoutovercoming the guiding stiffness of that wire and/or otherwise impingingon the vasculature walls with potentially injurious forces.

IAB catheters also must resist kinking, i.e., sharp bending collapse ofeither or both of the lumen tubes with attendant loss of smoothcurvature and closing or drastic reduction of the respective internalpassageway. Resistance to kinking is necessary to maintain pushabilityof the catheter assembly and to avoid binding on the guide wire.Avoiding kinking also minimizes risks of cracking of the lumens duringinsertion and attendant risks of later leakage during operation, as wellas minimizing risks of kink-blockage of the gas shuttle capacity betweenthe lumens or blockage of medication or sensing operations through theinner lumen during pumping operation.

It is an object of this invention to provide improved intra-aorticballoon pump catheters.

It is a more specific object of this invention to provide such catheterswherein adequate gas shuttling capacity can be obtained withconventional pump controllers through catheters of significantly reducedsize.

Similarly, it is an object of this invention to provide such improvedcatheters wherein substantially higher gas flow rates and attendanthigher shuttle speeds may be obtained in catheters of sizes usedheretofore, thereby permitting tracking of heart rhythms not trackablewith conventional previous catheters.

It is a further object to provide improved IAB catheters which attainsome or all of the aforegoing objects and which maintain high degrees offlexibility, torquability, pushability and trackability for safe andeasy insertion, with minimal risk of trauma to the patient.

SUMMARY OF THE INVENTION

It has been found that IAB catheters using very small metal lumen tubeshaving high degrees of elasticity and particularly shape restorativeelasticity will satisfy the aforementioned parameters. This will allowflexibility with stiffness over a wide range of bending angles of IABcatheters, down to quite severe bends and other temporary deformationswhich may occur in the course of insertion or operation. Moreparticularly, it has been found that by fabricating IAB catheters withat least the inner lumen being a superelastic thin walled metal tubesuch as of nitinol, the inner lumen can have a very thin wall with aninside diameter (ID) sufficient for a guidewire and a small outsidediameter (OD) which allows reduction of the outer lumen and relatedcomponents by at least one size Fr while providing gas shuttle capacitybetween the lumens for conventional IAB pump operation. This design alsoattains excellent flexibility and stiffness of the catheters for ease ofinsertion and assurance of functionality while reducing the outsidediameter to significantly reduce the risks of vascular and ischemiacomplications.

As used herein, the terms "superelastic alloy" or "superelastic alloys"and "superelasticity" refer to those materials, specifically those metalalloys, which return to their original shape upon unloading after asubstantial deformation. In most if not all instances superelasticity isrelated to shape memory. It is understood that a shape memory alloy isone which displays a thermoelastic martensitic transformation and isable to absorb several percent shear strain by preferential orientationof martensite variants, and then can reverse that shear strain uponbeing heated, as the martensite transforms back to the parent(austenits) phase. Similarly, it is understood that a superelastic alloyis the same as a shape memory alloy except that it absorbs strain abovethe transformation temperature by the creation of stress-inducedmartensite variants of preferential orientation, and then reverts to theparent phase at the same temperature as reduced stress reverses thestrain. Superelastic alloys can be strained up to ten times more thanordinary spring materials without substantial permanent deformation,i.e., less than 0.5%. They provide nearly constant stress forces over awide range of elastic deformation, as represented by typically "flagshaped" stress-strain curves, without significant change of temperature.

Nitinol (nickel-titanium alloys) is perhaps the best known of thesematerials. Its tranformational superelasticity is about ten times higherthan elasticity in ordinary materials. Further, various nitinol alloysare known which are superelastic within the temperature ranges of theliving human body. One further description of the superelasticitycharacteristic and of nitenol alloys which provide this characteristicat human body temperatures appears in a publication of RaychemCorporation entitled "Superelasticity--Superelastic Tinel® Alloys",which is incorporated herein by this reference and a copy of which isbeing filed with this application.

Further, it has been found that improved forms of the outer lumen may beprovided of co-extruded plastics to complement and enhance the sizereduction and capacity goals noted above. In the preferred embodimentthis includes a relatively thin major inner nylon portion for strengthand a polyurethane outer portion for biocompatability, flexibility andcompatibility for bonding to the balloon.

Improved techniques for production of appropriate balloons and forjoining the respective components also are provided, particularly forjoining of each balloon to the distal end of the outer lumen and to thedistal end of the inner lumen while avoiding or minimizing buildup ofdiametral dimensions. Moreover, it has been found that intra-aorticballoons may be made with thinner walls than heretofore to furthercomplement the aforenoted results without compromising the integrity ofthe system. A radiopaque metal marker ring also has been provided whichis compatible with the size reduction goal while providing improvedimaging capabilities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified top view of an intra-aortic balloon catheteremploying this invention.

FIG. 2 is an enlarged cross-sectional view taken along line 2--2 of FIG.1.

FIG. 3 is an enlarged cross-sectional view taken along line 3--3 of FIG.1, on a lesser scale than FIG. 2.

FIG. 4 is an enlarged side elevation view of the balloon portion of thecatheter with the balloon furled, such as for insertion.

FIG. 5 is an enlarged sectional view of a portion of the catheterassembly at the distal end of the balloon, taken along an axialdiametral plane.

FIG. 6 is an enlarged side view of the outer lumen and adjacent proximalend portion of the balloon of the catheter of FIG. 1.

FIG. 7 is an end view of a radiopaque tracer ring included in thecatheter of FIG. 1.

FIGS. 7A and 7B illustrate alternative configurations of the tracerring.

FIG. 8 is a side view of a stylet used in forming the guidewire of thecatheter of FIG. 1.

FIG. 9 is an enlarged side view of the outer end of the guidewire usedin the catheter of FIG. 1.

FIGS. 10A and 10B schematically illustrate the stripping of intra-aorticballoons from mandrels on which they have been formed by dip casting.

FIGS. 11A-E are schematic illustrations of steps for reforming theproximal end sleeve portions of such balloons.

FIG. 12 is a schematic side view of one preferred apparatus used in theprocess illustrated by FIGS. 11A-E.

FIG. 13 is a left-end view of the balloon clamp of FIG. 12.

FIG. 14 is a right-end view of the apparatus of FIG. 12.

FIG. 15 illustrates the shape of the cavity defined by the balloonclamp, as seen generally along line 15--15 of FIG. 13.

While the invention will be further described in connection with certainpreferred embodiments, it is not intended to limit the invention tothose embodiments. On the contrary, it is intended to cover allalternatives, modifications and equivalents as may be included withinthe spirit and scope of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As illustrated in FIG. 1, one embodiment of an intra-aortic balloon pumpcatheter device 10 includes a flexible outer lumen tube 12 and aco-axial flexible inner lumen tube 14 which are attached to a wyeconnector 16. The inner lumen tube 14 extends through the outer lumen 16and through a single chamber intra-aortic balloon 18 to the distal tipend of the catheter. The proximal end of the balloon 18 is attached tothe distal end of the outer lumen tube 12. The distal end of the balloon18 is attached to a compatible tip element 20 on the distal end of theinner lumen tube 14. Each of these balloon-lumen attachments is agas-tight solvent bond connection between an end sleeve section 21,22 ofthe balloon and the outer surfaces of the outer lumen 12 and the tip 20,respectively. As seen in the drawings, these end attachment sleeves areof substantially lesser diameter than the main displacement body section23 of the balloon and are joined thereto by short tapered sections24,25.

The wye connector 16 provides access through the lateral branch 26 to anappropriate gas supply pump and control device (not shown) for inflatingand deflating the balloon 20 by successively injecting and withdrawing agas such as helium through the annular space between the lumens 12 and14. As indicated above, this is sometimes referred to as "shuttling" theinflation gas to and from the balloon. The controller responds tosignals corresponding to the pulsing of the heart and effects inflationand deflation of the balloon in timed counterpulsation to the pumpingaction of the heart in a known manner. The axial section 27 of the wyeprovides axial access to the inner lumen for reception of a guide wire28 as well as for sensing of arterial pressure and/or the injection ofmedicaments through the inner lumen. Tie downs 32 are included foraffixation to the skin of the patient by suturing and/or taping forsecuring the catheter in its inserted operative pumping position.

The balloon 18 is a large flexible thin-film balloon of conventionalappropriate size, i.e., on the order of about 0.5" to about 1.0" indiameter when in an inflated but unstretched condition and about 8" to12" in length. Typical sizes are of 30 cc, 40 cc and 50 cc displacement.The balloon may be formed of any suitable material, with polyurethanepresently being preferred. A hydrophilic coating 36 preferably coversthe balloon and forms a lubricous outer surface which is very slipperywhen wetted by an aqueous fluid, such as blood, while permittingprocessing and furling of the balloon and handling of the balloon andrelated pump mechanism in a normal manner when dry. Presently preferredcoatings and appropriate modes of applying such coatings are disclosedin co-pending application Ser. No. 08/170,513, filed Dec. 20, 1993, thedisclosure of which is incorporated herein by this reference.

The balloon 18 is furled, as illustrated schematically at 18f in FIG. 4.This minimizes its effective outer diameter during insertion into apatient's arterial system. The furling may be accomplished in aconventional manner. This includes applying a solution of silicone andfreon on the outer surface such as by spraying to deposit siliconethereon, then evacuating the air from the balloon thereby causing theballoon to collapse into flat generally radially extending "wings", thenrolling those wings tightly about the inner lumen 14 in mutuallyinterleaved relation with one another. This winds the collapsed balloon"wings" into tightly packed spirals as viewed in cross-section, tominimize the effective outer diameter of the balloon during handling andduring the insertion process. The silicone avoids surface-to-surfacesticking of the furled layers. A thin tubular packaging sheath typicallyis placed over each furled balloon to maintain its furled compaction toa minimum effective outside diameter during shipping and handling, up tothe place and time of insertion into the patient. Further, the furledballoons typically are heated, e.g., to a temperature on the order ofabout 135° F. for about 12-16 hours, to assist in setting and therebysustaining the furling during insertion following removal from thepackaging sheath by the user. Balloons with the noted hydrophiliccoatings also become very slippery promptly upon being wetted, withattendant benefits of ease of insertion and placement as well asreduction of trauma.

The wye connector 16 and related components and equipment may be of anysuitable structure and size.

The inner lumen 14 is a very thin-walled tube formed of a tough andsuperelastic metal, namely nitinol. For example, it has been found thatan inner lumen tube 14 of such materials having a wall thickness of onlyabout 0.0035" will function satisfactorily in providing a small IABcatheter, e.g., 8 Fr size. The inner lumen tube 14 minimizes the outsidediameter of the inner lumen while maintaining the necessary functionalinside diameter as well as providing desirable characteristics offlexibility and strength throughout the length of the catheter.

An exemplary such inner lumen tube 14 has about 0.0276" ID and 0.0345"OD. By comparison, the inner lumen currently used in the 9 Fr IABcatheters being marketed by the Cardiac Assist Division of St. JudeMedical, Inc., under the trademark RediGuard™, consist of a polyurethanetube of about 0.008" wall thickness surrounded by a coiled stainlesssteel wire of 0.003" diameter generally as in the arrangement disclosedin U.S. Pat. No. 4,646,717, resulting in an effective overall thicknessof the inner lumen wall of 0.011" and an attendant OD of 0.054" toprovide an inner lumen ID of 0.032".

The outer lumen tube 12 is formed by coextrusion of a thin outerpolyurethane layer around a thicker nylon inner layer 12b. The nylonlayer provides high compressive strength relative to the thickness, andit is believed that the polyurethane layer provides flexibility as wellbiocompatability and compatibility for ready bonding of the polyurethaneballoon. One advantageous combination has been found to be a 0.002"outer layer of polyurethane coextruded with a 0.006" inner layer ofnylon, with the total wall thickness being about 0.008". Thus the outerlumen 12 also is a relatively thin-walled tube, as compared to currentcommercial polyurethane outer lumens which are on the order of 0.010"thick.

By utilizing inner and outer lumens 12 and 14 as described, the annularspace therebetween is of adequate cross-section to accommodate the gasshuttle capacity required for normal IABP operations using aconventional controller while minimizing the outside diameter of thecatheter, e.g., reduction of the catheter by one full size Fr, andmeeting the other desirable parameters for IAB catheters. Concomitantly,IAB catheters using this construction and of the same nominal size asprior constructions would be capable of higher gas shuttle rates thanthose prior devices and thus capable of tracking higher heart pulsationrates.

The outer lumen also could be formed of a thin walled metal tube havingsuperelasticity, for example also being formed of nitinol. Thisalternative would permit further reduction of the outer diameter of theouter lumen while maintaining equivalent or even better operationalcapabilities, but would add significantly to the costs at the presentprice of nitinol tubing. Referring particularly to FIGS. 8 and 9, theguidewire 28 is of a stylet-type with a "floppy J" tip, similar to someguidewires utilized heretofore in other applications, e.g. incholangiography (catheterization of bile ducts). The stylet 40 is a slimrod or wire which includes a main body portion 42 normally of uniformcircular cross-section and a distal end portion 44 of modifiedconfiguration for forming the "J" tip. For example, the distal endportion is significantly reduced in diameter along the second portion44, with an annular shoulder 46 between portions 42 and 44. Sequentiallyoutward of the section 44 is a third portion 48 which is tapered to alesser diameter, and an end portion 50 which is flattened incross-section. As represented in FIG. 9, the proximal end of a fine wire52 is brazed or welded to the stylet shaft adjacent the shoulder 46. Thewire extends in closely wound coil fashion about the distal portion 44,with the distal end being brazed or welded to the distal tip of thestylet body 42. The distal end portion 50a is bent approximately 180°,preferably being bent normal to the flattening planes, to form the bightof the "J" tip, generally as illustrated.

By way of further example, one guidewire 28 for use in one specificembodiment of this invention as described herein included a stylet 40formed of 302/304 stainless steel, about 150 cm in length and with theshoulder 46 being about 30 cm from the distal end. The main body portion42 was about 0.025" in diameter. Second portion 44 was about 0.013" indiameter and extended for about 23 cm from the shoulder 46. Portion 48was tapered from the 0.013" diameter to about 0.0055" diameter over alength of about 6 cm, and the distal end 3 cm portion was flattened toabout 0.0035" thickness. The wire 52 was about 0.005" diameter, alsobeing of 302/304 stainless steel. The distal 3 cm was bent to form thebight and remote leg of the "J" tip. The entire assembly was coated withTeflon, providing a guidewire with a diameter not exceeding 0.025" foruse through the inner lumen described above.

As noted above, the balloon 18 may be of the same material,configuration and size as balloons currently in use in intra-aorticballoon pumps. An example of a preferred embodiment includes athin-walled polyether based polyurethane balloon of about 0.003"-0.004"wall thickness formed by dip molding on an appropriately shaped mandrel,with a hydrophilic coating as referred to above. This is a reduction ofabout 0.001 thickness from balloons currently in commercial use. Suchballoons have satisfactory flexibility and strength, with highelasticity, e.g., about 525% stretchability without rupture. Onespecific commercially available polyurethane which has provensatisfactory in such balloons, including those used in practicing thisinvention, is sold by B. F. Goodrich under the designation "Estane58810".

Referring particularly to FIG. 5 an end tip 20 is affixed over the outerend of the inner lumen tube 14, as by being molded thereonto. For thispurpose, the outer surface of the end portion of the tube may besandblasted as a preparatory step. The tip 20 preferably is of a plasticwhich is compatible with the material of the balloon, e.g.,polyurethane. The outer end surface 62 of the tip is rounded in abullet-nose shape to facilitate passage through the patient'svasculature. The outer end portion has a central axial passage 64 whichprovides a smooth continuation of the central axial passage of the lumentube 14 and preferably tapers or flares toward the distal end of thetip, as illustrated in FIG. 5. This passage section 64 may be formed bya core pin being positioned in the outer end of the lumen tube 12 priorto the molding of the tip 20.

Referring now to FIGS. 1, 5 and 6, the cylindrical proximal sleeveportion 21 of the balloon 18 is bonded to the outer surface of thedistal portion of the outer lumen 12 and the cylindrical distal sleeveportion 22 of the balloon is bonded to the outer surface of the tip 20.These bonds must be airtight and effected in a manner to minimize thediametral dimension build-up of the catheter assembly. Such bonding isfacilitated by forming the tip 20 and at least the outer surface of theouter lumen 12 and the balloon 18 of the same types of materials, namelypolyurethane in the illustrated preferred embodiment. In thisembodiment, the sleeve portions 21 and 22 are bonded to the respectiveelements by a solvent and pressure-bonding technique. It is believedthat pressure-bonding with radiofrequency heating to a temperatureapproximating the melting temperature of the materials will furtherenhance this bond and provide even greater control and minimizing of thefinal outer dimensions in these bonding areas. The intervening portionof the balloon 18, including the larger body section 23, is tightlyfurled about the inner lumen tube 14 between the distal end of the innerlumen 12 and the tip 20. With the thin-walled balloon referred to above,this multi-layered furled portion will have an outer diameter which onlyslightly exceeds the outer diameter of the sleeve attachment sections.This is an added factor in maintaining the minimal profile of the entirecatheter assembly during insertion.

Referring to FIGS. 10A and 10B, the balloons 18 are made by dip castingon a mandrel 66 having a shape corresponding to the inflated unstretchedshape of the balloon 18, including the end sleeve sections 21,22,generally as seen in profile in FIG. 1 and 10A. The dipping speed andtime are adjusted to produce thin-walled balloons as referred to above.Each of the balloon blanks as thus formed also includes an end section Swhich extends from the sleeve 21 over the mandrel hanger generally asillustrated, and which subsequently is trimmed from the blank. Theformed balloons are stripped from the respective mandrels by axialmovement toward the distal end, whereby the proximal sleeve 21 andadjacent tapered portion 24, as well as section S, are stretched indiameter as they slide over the much larger central portion of themandrel on which the main balloon body portion 23 was formed, asillustrated schematically in FIG. 10B. This stretching of the proximalends results in proximal end sleeves that are not reliably of asufficiently small inner diameter to provide the desired snug fit of theballoon on the small outer lumen tubes 12 for facile formation of thenecessary air-tight joint at this interface. Accordingly, the productionof the balloons preferably includes reduction of the size of theproximal end sleeves after removal of the balloons from the castingmandrels.

Referring to FIGS. 11A-11E and 12, the section S and sleeve portion 21of each balloon blank are mounted over an internal mandrel 70 andsecured in place by a collet 72. The balloon is stretched to apredetermined length of the proximal sleeve section 21, as indicated bythe arrow A in FIG. 11A. The balloon then is held in the stretched stateto maintain the desired sleeve length, as by a hinged clamp 74 whichengages the cone section 24 of the balloon, as in FIG. 11B. Thestretching causes the intervening sleeve to neck down to the desiredreduced diameter, as indicated in FIGS. 11A and 11B. At this point theneck is in a stressed state. At least the sleeve section of the balloonis heated, as by an internal heater cable 76 which is positioned withthe mandrel 70 (see FIG. 11C), to an appropriate temperature over anappropriate dwell time thereby relaxing the necked-down balloon materialin its reduced size configuration. That is, the stress induced by thestretching is relieved. The balloon then is permitted to cool to anormalizing temperature while in the reduced, non-stressedconfiguration, as by turning off the power to the heater; see FIG. 11D.This precludes subsequent elastic return of the sleeve portion 21 to itsprevious oversize diametral dimension. The balloon with the reduceddiameter proximal end sleeve 21 then is removed from the clamp andmandrel, and the end section S is trimmed off as in FIG. 11B.

One mechanism for effecting the foregoing is illustrated in somewhatgreater detail in FIGS. 12-15. A mandrel 70 is mounted in a supportblock 82 which is pivotally mounted to a fixed support 84 as by anappropriate pivot pin 86 located adjacent one end of the block 82, withthe pivot pin offset from the mandrel 70. The heating cable 78 extendsthrough the mandrel 70 to a pin shaped heating element 76. Anintervening portion of the mandrel 70 has a bulbous section 88, with anannular outer surface 89 which tapers to smaller diameters toward thesupport block 82. The collet 72 is of an annular or "washer" shape,having an internal surface which conforms to the tapered surface of themandrel. The clamp 74 comprises two hinged mating halves definingtherebetween a truncated conical open section 90 communicating with ashort small cylindrical section 92, which correspond generally to theconfiguration of the transitional section 24 and desired sleeve section21 of the balloons being processed.

In operation, to practice the aforedescribed method, the clamp 74 isopened in preparation for receiving a balloon to be processed. Thecollet 72 is retracted toward the heater cable base block 82. The block82 is pivoted to an upper position (about 90° counterclockwise) in FIG.14, to raise the mandrel/heater further from a support surface on whichthe components are mounted and thereby providing greater space for thefollowing described manipulations. The distal end portion of a balloonthen is slid onto the mandrel unit 70, from the left end in FIG. 12,with the distal end portion of the sleeve section S over the enlargedsection 88 and onto the tapered section 89. The collet 72 is then movedtowards the enlarged section 88, to provide friction clamping of theballoon end S between the inner surface of the collet and the outertapered surface of the mandrel. The balloon is then stretched, e.g.manually by the operator, to the point where the tapered end section 24will match up with the cavity defined by the sections 90 of the clamphalves, thereby suitably reducing the diameter of the neck or sleevesection 21. The heater cable base block 82 is closed, and the balloon ispositioned with the tapered end section 24 mating into the cavitydefined by the sections 90 of the clamp halves, with the sleeve sectionstretched over the intervening internal mandrel and heater 76. The clamp74 then also is closed to retain the sleeve section of the balloon inthe resulting stretched state. Internal to the balloon at this point isthe heater coil 76, which extends the entire length of the sleeve areaand slightly into the balloon body area, as seen in FIG. 12.Subsequently, the heater is activated to thereby relax the necked downballoon material as described above. Following heating and subsequentcooling, the clamp 74 is opened and the collet 72 released, and theballoon is removed. The section S then is cut off. A distal end portionof the stretched sleeve also may be trimmed to attain the desired lengthof sleeve 21 which now has the desired reduced inner diameter. Theinternal mandrel/heater may be utilized as the form for setting the sizeof the reformed sleeve section 21. By way of more specific example, in atypical operation the sleeve portion 21 has been stretched to about 150%of its original length in this process, e.g., stretched from 0.5" to0.75," to effect the desired reduction of the diameter of the neck inpolyurethene balloons as described hereinabove.

It will be appreciated that other gripping and stretching mechanisms maybe utilized to effect the sleeve sizing method. For example, one and/orthe other of the clamping mechanisms 74 and 72,88 may be movable towardand away from the other whereby the balloon blank may be clamped thereinprior to stretching and then may be stretched by lateral movement of oneor both of the clamping mechanisms relative to the other.

Referring to FIGS. 6 and 7, radiopaque marker material is applied to theouter lumen 12 in a position to be adjacent the proximal end of theballoon in the final assembly. This permits the user to readilydetermine the location of the balloon by fluoroscopy or X-ray, asnecessary to attain maximum therapeutic benefit. In a preferredembodiment this marker is a thin short ring 94 of highly elastic metalsuch as nitinol, being the same material as the inner lumen. Use of thesame metal for the marker and the lumen avoids any problems ofincompatibility of dissimilar metals, such as electrokinetic corrosionof either element, while providing a highly radiopaque and thereforehighly visible marker for the positioning of the IAB during use. Byusing a thin short ring 94 of nitinol, e.g. 0.003" thick and 0.075"long, the marker may be press-fit in place in the outer lumen 12 and thecompression of the lumen will hold the ring in place. The balloon isbonded over the outer lumen 12, preferably with the sleeve 21 of theballoon over the marker ring 94, and is furled tightly over the innerlumen tube 14 as noted above. The high degree of elasticity of the ringpermits the marker to deform in the process of packaging and insertionwhile assuring return to its nominal desired shape and size in use.Splitting the ring longitudinally so that it is discontinuouscircumferentially, with the ends either spaced or overlapping asillustrated at 94a and 94b in FIGS. 7A and 7B respectively, will enhanceits hoop compressibility by a resilient spring action and thus furthercomplement the size reduction as well as flexibility of the catheterunit.

In a specific example of the preferred embodiment of this invention, anominal 8 Fr IAB catheter 10 was fabricated with an inner lumen tube 14formed of a nitinol alloy tubing of Raychem Corporation designated TinelAlloy BB formed of only nickel and titanium and only those traceelements naturally occurring in commercially available grades of thoseconstituents. The tube 14 had a nominal inner diameter of 0.0276" anominal outer diameter of 0.0345", and a length of 32.775". The outertube 12 was a coextrusion of 2363-55D Pelletbane polyurethane (DowChemical Company, Midland, Mich.) 0.002" thick over Nylon 11 Besno (ElfAtochem, Philadelphia, Pa.) 0.006" thick, as described above, with anominal inner diameter of 0.090" and a nominal outer diameter of 0.108".The tip and guide wire used in the catheter were as described above, andthe balloon was of 0.003" nominal thickness. The balloon was furled to adiameter of 0.118" and could relax to about 0.124" diameter in itspackaging sheath.

Testing

Kink tests and stiffness tests were conducted on inner and outer lumensand the combination of the two as described above, with only slightlydifferent dimensions. The nitinol inner lumens tested had an innerdiameter of 0.0283"±0.0003" and an outer diameter of 0.0347"±0.0003. Thecoextruded outer lumens had a nominal inside diameter of 0.090" and anominal outside diameter of 0.106". Crush tests also were conducted onvarious outer lumens.

The kink tests utilized a template having multiple circles imprintedthereon, all with a common tangent point. The circles were 2", 13/4",11/2", 11/4", 1", 3/4" and 1/2" in diameter. An appropriate length ofeach tubing being tested was formed into a larger loop and held againstthe template with the ends crossing and tangent to the circles at theaforenoted common tangent point. While maintaining this relationship tothe template, one end of the looped tube was pulled to gradually reducethe loop diameter until the sample kinked. The diameter, also in inches,at which kinking occurred was recorded. When the tubing kinked betweentwo circles, the average of those two circles was used as the kinkdiameter for calculations. In the case of outer lumen tubes, notes alsowere made of whether the kinking occurred quickly, moderately or slowly.

After examining a variety of potential 8 Fr outer lumens, sevencoextrusions of polyurethane over nylon were tested, along with one 9 Frouter lumen as described above for comparison purposes, using fivesamples of each. The following table reflects the average diameter, ininches, at which kinking occurred in each of these seven prospectiveouter lumens, the nature of the kinking action, and the averagediameter, also in inches, at which the combination of the respectiveouter lumen tube and a nitinol inner lumen as described above kinked:

    ______________________________________                                        Lumen-Coextrusion                                                                            OUTER LUMEN ONLY    COMBINED                                   Materials      Diameter Notes      Diameter                                   ______________________________________                                        a.  .003" nylon,   1.38     Moderate 1.5                                          .005" polyurethane                                                        b.  .005" nylon,   1.53     Quickly  1.6                                          .003" polyurethane                                                        c.  .004" nylon,   1.65     Quickly  1.75                                         .004" polyurethane                                                        d.  .001" nylon,   1.0      Slowly   1.15                                         .007" polyurethane                                                        e.  .002" nylon,   1.05     Slowly   1.3                                          .006" polyurethane                                                        f.  .004" nylon    1.73     Quickly                                               .004" polyurethane                                                            (with barium sulfate)                                                     g.  .006" nylon,   1.18     Quickly  1.33                                         .002" polyurethane                                                        ______________________________________                                    

The 9 Fr outer lumen tubes were of the aforedescribed current commercialdesign, being polyurethane tubes with an inner diameter of about 0.101"and an outer diameter of about 0.122". The average first kinkingdiameter for the 9 Fr outer lumen tubes was 1" and they kinked "slowly".

The three outer lumens with the best kink test results, namelycoextrusions d, e and g, also were tested for crush resistance inhemovalves. The coextrusion g provided the best resistance to crushingby the valves.

Further samples of the construction g, namely coextrusion tubes of0.002" polyurethane around 0.006" nylon, were subjected to furthercomparative tests with samples of the aforedescribed 9 Fr catheter lumentubes, singly and in combination of the respective inner and outer lumentubes. The average kink diameters in inches were as follows:

    ______________________________________                                                        New 8 Fr                                                                              Current 9 Fr                                          ______________________________________                                        Inner Lumen Tube* Less than 0.5                                                                           Less than 0.5                                     Outer Lumen Tube  1.35      1.15                                              Combination of the Above                                                                        1.19      1.15                                              ______________________________________                                         *The nitinol tubes tested included both extruded tubes and drawn and          machined tubes, with the results being substantially the same.           

Thirty samples each of the new inner and outer lumen tubes and ten eachof the inner and outer tubes of the current design were subjected tostiffness tests, both individually and with the respective inner andouter tubes assembled together, using a Tinius Olsen stiffness tester.The bending moments were calculated and used for comparisons. Since theareas of the 8 Fr and 9 Fr parts were different, the values werenormalized by multiplying the 9 Fr results by the ratios of their areas.Selected comparison angles were chosen within the following parameters:(1) All samples achieved the angle; and (2) the test data had notstarted to decline, i.e., no indication of a kink forming in the sample.The average values in inch-pounds were as follows:

    ______________________________________                                                    Bending Moment                                                                            Bending Moment                                        ______________________________________                                        Inner Lumen   at 57 Degrees                                                   ______________________________________                                        New Inner Lumen                                                                             0.265                                                           Current Inner Lumen                                                                         0.014                                                           ______________________________________                                        Outer Lumen   at 27 Degrees                                                   ______________________________________                                        New Outer Lumen                                                                             0.168                                                           Current Outer Lumen                                                                         0.075                                                           ______________________________________                                        Combined Lumen                                                                              at 69 Degrees at 57 Degrees                                     ______________________________________                                        New Outer/lnner Lumen                                                                       0.433         0.413                                             Current Outer/Inner Lumen                                                                   0.115         0.144                                             ______________________________________                                    

It will be seen that the constructions in a accordance with thisinvention attained the desired size reduction, while providing good kinkresistance and attendant flexibility and increased stiffness.

Thin-walled balloons as alluded to above also were tested foroperational strength, using thirty sample uncoated balloons with anaverage measured thickness of 0.0033" (range of 0.003" to 0.004") andthirty such balloons with a hydrophilic coating and therefor having anaverage measured thickness of 0.0037" (range of 0.003" to 0.004"). Testsusing samples of the respective materials showed average yield strengthsof 1070 psi for the uncoated material and 889 psi for the coatedmaterial. The corresponding internal pressures to generate yieldpressures, in a 40 cc IAB for example, would be 11.15 psi for theuncoated material and 10.33 psi for the coated material.

Aneurysm tests also were conducted using such sample balloons which wereadhered to outer lumens and leak tested prior to being subjected toaneurysm pressures. Pressure was increased in each balloon until adramatic reduction of pressure was noted, indicating rapid expansion ofthe balloon membrane. The average aneuryzation pressures so measuredwere 13.6 psi for the uncoated balloons and 10.58 psi for the coatedballoons. Thus, all were far above the normal usage pressure of about150 mmHG or 2.9 psi for such balloons, by a factor of more than three.

It will be appreciated that improved intra-aortic balloon pump deviceshave been provided which meet the objects of this invention.

The invention has been described in considerable detail with referenceto certain embodiments, and particularly with respect to the preferredembodiments thereof. However, it will be understood that variations,modifications and improvements may be made, particularly by thoseskilled in this art and in light of the teachings referred to herein,within the spirit and scope of the invention as claimed.

What is claimed is:
 1. A method of forming intra-aortic balloons forassembly in vascular catheter systems comprising the steps of forming aballoon blank having a sleeve section at one end, stretching such sleevesection longitudinally to reduce the diameter thereof, heating saidstretched sleeve section to relieve the stress in said sleeve sectionwhile so stretched, and cooling said sleeve section, thereby to preservesaid sleeve section in its reduced diameter state wherein said balloonblank including said reduced diameter sleeve section forms saidintra-aortic balloon.
 2. The invention as in claim 1 wherein saidballoon blank is formed of plastic by dip casting on a mandrel.
 3. Theinvention as in claim 1 including the steps of forming said balloonblank by dip casting a plastic material on a mandrel with said sleevesection being formed on said mandrel at one end of said blank, andremoving said blank from said mandrel by axial sliding over said mandrelin a direction wherein said sleeve section is stretched over saidmandrel in the course of such removal.
 4. The invention as in claim 1wherein said stretching step is carried out by gripping a first portionof said balloon blank at the distal end of said sleeve section, grippinga second portion of said balloon blank at the opposite end of saidsleeve section, and moving at least one of said gripped portions awayfrom the other.
 5. The invention as in claim 4 wherein said firstportion is gripped between an internal mandrel and a surrounding clamp,and said second portion of said balloon is gripped in a clamp.
 6. Theinvention as in claim 5 wherein stretching step is carried out prior toengagement of said second portion in said clamp.
 7. The invention as inclaim 5 wherein said stretching step is carried out by moving one ofsaid mandrel and said clamp away from the other after said balloonportions are gripped therein.
 8. The invention as in claim 4 andincluding positioning a heating element within said sleeve section, andwherein said heating step is effected by said heating element fromwithin said sleeve section.
 9. The invention as in claim 1 and whereinsaid heating step is effected by a heating element disposed interiorlyof said sleeve section.